T cells recognize tumors or infected cells and prevent onset of disease by killing these target cells. However, the interplay of tumors or pathogens and the immune system is complex, as demonstrated by cancer or chronic infections developing in the presence of specific T cells, whereby the pathogens or tumors obviously could evade T-cell surveillance.
The ability of T cells to detect virtually any pathogenic invader is granted by its extraordinarily diverse receptor repertoire, which allows the T-cell pool to recognize a vast number of peptides upon presentation by major histocompatibility complex (MHC) molecules. Still, signaling through the T-cell receptor (TCR) (signal 1) is not sufficient for adequate T-cell activation, as costimulatory molecules provide indispensable signals for proliferation, survival, and differentiation (signal 2). In fact, naive T cells that only receive signal 1 without signal 2 are rendered anergic (unresponsive) or die through apoptosis. The integration of signals 1 and 2 is required for full T-cell activation, and the strength of these signals shapes the size of the ensuing T-cell pool. Moreover, full differentiation into effector T cells is generally dependent on a third signal, which is supplied by the antigen-presenting cell (APC) in soluble form and provides instructive signals for the type of effector T cell that is required. This ‘three-signal’ concept depicts a model for the activation of naive T cells and the subsequent formation of effector T cells. Yet, the immune system provides a plethora of diverse costimulatory molecules and these various types of signal 2 and 3 all contribute in their own unique manner to the quality of the T-cell response. Costimulatory signals and soluble forms of signal 3 can act on particular aspects of T-cell activation, such as survival, cell cycle progression, type of effector cell to be developed, and differentiation to either effector or memory cell.
It is now generally accepted that mature antigen-presenting dendritic cells (DCs) have to be “helped” by other lymphocytes, including CD4+ T cells NK cells and NKT cells, in order to induce long-lived memory CD8+ T cells. This “help” induces the mature DCs to differentiate further, a process known as licensing. “Helper” signals has multiple effects on DCs, including the upregulation of costimulatory molecules, the secretion of cytokines, and the upregulation of several antiapoptotic molecules, all of which cumulatively potentiate the ability of DCs to optimally activate cognate T cells, especially CD8+ T cells. Moreover, “helper” lymphocytes may also express or secrete factors that directly affect T cell survival, cell cycle progression, type of effector cell to be developed, and differentiation to either effector or memory cell.
One strategy for fighting chronic infections or aggressive cancer is adoptive T-cell therapy, which involves the transfer of effector T cells to restore specific T-cell responses in the host. Recent technical developments to obtain T cells of wanted specificities have created increasing interest in using adoptive T-cell therapy in different clinical settings. Adoptive cell transfer therapy is the administration of ex vivo activated and expanded autologous tumor-reactive T cells. There are several potential advantages with the use of adoptive cell transfer therapy in cancer treatment. Tumor specific T cells can be activated and expanded to large numbers ex vivo, independently of the immunogenic properties of the tumor, and functional and phenotypic qualities of T cells can be selected prior to their adoptive transfer.
After adoptive transfer, several events must occur for T cells to cause the regression of established tumors. More specifically:—T cells must be activated in vivo through antigen specific restimulation, —the T cells must then expand to levels capable of causing the destruction of significant tumor burdens, —antitumor cells must survive long enough to complete the eradication of all tumor cells.
Previously, the criterion used to selecting cells for adoptive transfer to patients with solid tumors was the ability of the antitumor T cells to release IFN-γ and kill tumor cells upon coculture. However, it is now clear that these criteria alone do not predict in vivo efficacy. Gattinoni et al., J. Clin. Invest. 115:1616-1626 (2005), found that CD 8+ T cells that acquire complete effector properties and exhibit increased antitumor reactivity in vitro are less effective at triggering tumor regressions and cures in vivo.
Methods according to prior art requires restimulation one or more times to reach clinically relevant levels of tumor specific cytotoxic T cells. See for example Ho et al. (Journal of Immunological Methods, 310(2006), 40-50) and Gritzapis et al. (J. Immunol., 2008; 181; 146-154) wherein restimulation 1-2 times were necessary to reach a level of tumor specific CD8+ T cells of about 19%. Restimulation makes the cells less active and closer to apoptosis.
Consequently, there is a need for a method of preparing a T cell population for use in adoptive immunotherapy that increases proliferation and survival of antigen-specific T cells during their activation.